1. Field of the Invention
The present invention relates to a rotor type open-end spinning unit. More particularly, this invention relates to a spinning frame that has an outer rotor, which is provided with a collecting section for collecting opened fibers supplied, and an inner rotor, which is provided inside the outer rotor and is driven independently of the outer rotor.
2. Description of the Related Art
In an ordinary rotor type open-end spinning frame, a supplied sliver is opened by a combing roller and foreign matter is expelled. The opened fibers are supplied into a rotor by an airstream produced in a fiber transport channel due to negative pressure in the rotor, that rotates at a high speed. The fibers are then collected at a fiber-collecting section at the largest inner diameter portion of the rotor. The collected fibers are drawn from a guide hole or a yarn drawing passage, provided in the center of a navel, by a draw roller, and is simultaneously twisted in accordance with the rotation of the rotor to form a yarn. The yarn is then wound around a bobbin as a package.
It is known that open-end spinning frames have a higher productivity than ring spinning frames. In general, however, a fabric woven with yarn produced by an open-end spinning frame (hereinafter called open-end yarn) has a poorer texture than a fabric woven with yarn produced by a ring spinning frame (hereinafter called ring yarn). When fibers flown into the twisting area are wound around yarn that is being formed, the appearance of the yarn is deteriorated. Further, the open-end yarn has a lower strength than the ring yarn.
The present inventor thought that the poor texture of the manufactured fabric could be the result of the difference in structure between the open-end yarn and the ring yarn. The conventional open-end yarn has a prominent rough surface as if formed by twisting a ribbon or a tape, whereas the ring yarn has a relatively smooth outer surface. This may be because, in the conventional open-end spinning frame, as shown in FIG. 26, a fiber bundle F to be drawn to the guide hole (not shown) from a fiber-collecting section 72 of a rotor 71 is drawn from a separation point P almost vertically to the inner wall of the rotor 71. Because the angle .theta. between the fiber bundle F (yarn Y) at the separation point P and the inner wall of the rotor 71, or the twisting angle .theta. with respect to the fiber bundle F, is substantially 90 degrees, the fiber bundle F is bent by nearly 90 degrees so that tension is always applied to the outer fiber at the bent portion of the fiber bundle F while the inner fiber become slack. As the fiber bundle F is twisted under this condition, yarn is formed with fibers with lower tension wound around higher-tension fibers located at the center. As a result, the produced yarn becomes wavy and prominently shows a rough outer surface.
As a solution to the shortcoming of the conventional open-end yarn, another apparatus is disclosed in Japanese Unexamined Patent Publication No. 51-64034. This apparatus has a rotor having a fiber-collecting section or an outer rotor, and a draft rotor or an inner rotor, which is provided inside the outer rotor. This apparatus has a yarn drawing hole for drawing a fiber bundle collected at the collecting section and makes a differential rotation with respect to the outer rotor.
As shown in FIG. 27, this apparatus has an inner rotor 74 concentrically provided inside an outer rotor 73. The inner rotor 74 rotates slightly faster than the outer rotor 73 and the fiber bundle F is drawn through a yarn drawing hole 75 of the inner rotor 74. Accordingly, this apparatus spins out the fiber bundle F while drafting it. The aforementioned publication also discloses an apparatus that has a small disk 76, which is attached to the inner rotor 74 and revolves and rotates while being pressed against the fiber bundle F collected at the collecting section, as shown in FIG. 28(a). This apparatus spins out the fiber bundle F while drafting it with the floating of the fiber bundle F suppressed.
When the rotation speeds of both rotors 73 and 74 in the apparatus shown in FIG. 27 are relatively low, about 30,000 rpm, the fiber bundle F separated from the collecting section can be spun out along a gentle curve from the separation point P to the yarn drawing hole 75 as indicated by the solid line in FIG. 27. When the rotational speeds of the rotors become as fast as about 90,000 rpm, however, the fiber bundle F moving toward the yarn drawing hole 75 from the collecting section is stretched straight to very near the collecting section by the increased centrifugal force as indicated by the chain line. Consequently, the twisting angle becomes approximately 90 degrees, raising the above-discussed problem of the conventional open-end spinning frame having no inner rotor 74.
In the apparatus with the small disk 76 as shown in FIG. 28(a), it is possible to set the separation point P at a position immediately downstream of the position where the small disk 76 presses the fiber bundle F against the collecting section as shown in FIG. 28(a) by increasing the yarn drawing speed (winding speed) to increase the draft ratio when the rotational speed of the rotor becomes high. However, if the draft ratio is increased, the pressure by which the fiber bundle F contacts a point D of the end portion of the yarn drawing hole 75 raises so that twisting is hardly transmitted upstream from the point D, as shown in FIG. 28(b). This prevents the fibers collected at the collecting section from being drawn out. When the twisting force is increased to transmit twisting to the separation point P, bridge fibers Fb are produced between the inlet of the yarn drawing hole 75 and the point P and are wound around the fiber bundle F in a coil form. This yields so-called neck-wound fibers, which deteriorate the appearance of the yarn. This yarn reduces the texture quality of a fabric that is produced with the yarn.
When the pressure at which the small disk 76 contacts the outer rotor 73 is large, the inner rotor 74 causes the outer rotor 73 to rotate, making it difficult to rotate the inner rotor 74 and the outer rotor 73 with a predetermined speed difference. As the small disk 76 rotates while being in contact with the outer rotor 73, the small disk 76 or the outer rotor 73 is likely to wear.